قَالَ سَنَشُدُّ عَضُدَكَ بِأَخِيكَ
Allah said;We will strengthen your arm through your brother,
meaning, `We will add strength to your cause and give you help through your brother, who you have asked to be made a Prophet alongside you.'
This is like the Ayat;
قَدْ أُوتِيتَ سُوْلَكَ يمُوسَى
You are granted your request, O Musa! (20;36)
وَوَهَبْنَا لَهُ مِن رَّحْمَتِنَأ أَخَاهُ هَـرُونَ نَبِيّاً
And We granted him his brother Harun, (also) a Prophet, out of Our mercy. (19;53)
One of the Salaf said,
"There is no one who has ever done a greater favor to his brother than Musa did for Harun, may peace be upon them both, for he interceded for him until Allah made him a Prophet and Messenger with him to Fir`awn and his chiefs."
Allah said concerning Musa;
وَكَانَ عِندَ اللَّهِ وَجِيهاً
he was honorable before Allah. (33;69)
وَنَجْعَلُ لَكُمَا سُلْطَانًا
and (We will) give you both power,
means, overwhelming evidence.
فَلَ يَصِلُونَ إِلَيْكُمَا بِأيَاتِنَا
so they shall not be able to harm you, with Our Ayat;
means, `they will have no way or means of harming you because you are conveying the signs of Allah.'
This is like the Ayat;
يَا أَيُّهَا الرَّسُولُ بَلِّغْ مَا أُنزِلَ إِلَيْكَ مِن رَّبِّكَ وَإِن لَّمْ تَفْعَلْ فَمَا بَلَّغْتَ رِسَالَتَهُ وَاللّهُ يَعْصِمُكَ مِنَ النَّاسِ
O Messenger! Convey what has been sent down to you from your Lord. And if you do not, then you have not conveyed His Message. Allah will protect you from mankind. (5;67)
الَّذِينَ يُبَلِّغُونَ رِسَالَاتِ اللَّهِ وَيَخْشَوْنَهُ وَلَا يَخْشَوْنَ أَحَدًا إِلاَّ اللَّهَ وَكَفَى بِاللَّهِ حَسِيبًا
Those who convey the Message of Allah and fear Him, and fear none save Allah. And sufficient is Allah as a Reckoner. (33;39)
And sufficient is Allah as a Helper and Supporter. And Allah told them the consequences in this world and the next, for them and for those who followed them,
أَنتُمَا وَمَنِ اتَّبَعَكُمَا الْغَالِبُونَ
you two as well as those who follow you will be the victors.
This is like the Ayat;
كَتَبَ اللَّهُ لاّغْلِبَنَّ أَنَاْ وَرُسُلِى إِنَّ اللَّهَ قَوِىٌّ عَزِيزٌ
Allah has decreed;"Verily, it is I and My Messengers who shall be the victorious."
Verily, Allah is All-Powerful, All-Mighty. (58;21)
إِنَّا لَنَنصُرُ رُسُلَنَا وَالَّذِينَ امَنُوا فِي الْحَيَاةِ الدُّنْيَا وَيَوْمَ يَقُومُ الاَْشْهَادُ
Verily, We will indeed make victorious Our Messengers and those who believe in this world's life and on the Day when the witnesses will stand forth, -- (40;51